rest_framework解析器组件源码流程
解析器顾名思义就是对请求体进行解析。为什么要有解析器？原因很简单，当后台和前端进行交互的时候数据类型不一定都是表单数据或者json，当然也有其他类型的数据格式，比如xml，所以需要解析这类数据格式就需要用到解析器(也可以将请求体拿到，然后利用其他模块进行解析)。
rest_framework解析器就是对你请求体中的数据进行反序列化、封装 把你的所有的请求数据都封装在request.data中 以后就在request.data中获取数据
源码分析
在APIView的dispatch方法中重新封装了request
request = self.initialize_request(request, *args, **kwargs)
执行initialize_request()方法，在该方法中，get_parsers用于获取解析器，并被封装到request.parsers中。
def initialize_request(self, request, *args, **kwargs):
"""
Returns the initial request object.
"""
parser_context = self.get_parser_context(request)#
return Request(
request,
parsers=self.get_parsers(), #获取所有的解析器，封装到request.parsers中
authenticators=self.get_authenticators(),
negotiator=self.get_content_negotiator(),
parser_context=parser_context
进入get_parsers()源码
def get_parsers(self):
"""
Instantiates and returns the list of parsers that this view can use.
"""
return [parser() for parser in self.parser_classes] #列表生成式，返回解析器对象，self就是当前执行APIview的类
进入parser_classes源码
class APIView(View):
# The following policies may be set at either globally, or per-view.
renderer_classes = api_settings.DEFAULT_RENDERER_CLASSES
parser_classes = api_settings.DEFAULT_PARSER_CLASSES #解析器全局配置
authentication_classes = api_settings.DEFAULT_AUTHENTICATION_CLASSES
throttle_classes = api_settings.DEFAULT_THROTTLE_CLASSES
permission_classes = api_settings.DEFAULT_PERMISSION_CLASSES
content_negotiation_class = api_settings.DEFAULT_CONTENT_NEGOTIATION_CLASS
metadata_class = api_settings.DEFAULT_METADATA_CLASS
versioning_class = api_settings.DEFAULT_VERSIONING_CLASS
进入api_settings源码
api_settings = APISettings(None, DEFAULTS, IMPORT_STRINGS)# api_settings是APISettings类实例化的对象
进入APISettings源码
寻找parser_classes，在api_settings中找不到DEFAULT_PARSER_CLASSES，所以在APISettings中找，还是找不到，所以运行__getattr__方法。
__getattr__函数的作用： 如果属性查找（attribute lookup）在实例以及对应的类中（通过__dict__)失败， 那么会调用到类的__getattr__函数, 如果没有定义这个函数，那么抛出AttributeError异常。
@property def user_settings(self): if not hasattr(self, '_user_settings'): self._user_settings = getattr(settings, 'REST_FRAMEWORK', {}) return self._user_settings def __getattr__(self, attr): #找不到DEFAULT_PARSER_CLASSES，所以运行__getattr__函数 if attr not in self.defaults: raise AttributeError("Invalid API setting: '%s'" % attr) try: # Check if present in user settings val = self.user_settings[attr] except KeyError: # Fall back to defaults val = self.defaults[attr] # Coerce import strings into classes if attr in self.import_strings: #这个函数就是首先将要导入的路径名分割成模块名和类名，然后再来从模块中获得到类这个属性，然后就完成了 val = perform_import(val, attr) # Cache the result self._cached_attrs.add(attr) setattr(self, attr, val) return val
进入DEFAULTS源码
DEFAULTS是rest_framework的默认settings配置文件，是个大字典，其中就有解析请求头的解析器
'DEFAULT_PARSER_CLASSES': (
'rest_framework.parsers.JSONParser',
'rest_framework.parsers.FormParser',
'rest_framework.parsers.MultiPartParser'
),
当调用request.data获取请求数据时候将使用解析器，下面是request.data源码：
@property
def data(self):
if not _hasattr(self, '_full_data'):
self._load_data_and_files() #执行_load_data_and_files()，获取请求体数据获取文件数据
return self._full_data
进入_load_data_and_files()源码
def _load_data_and_files(self): """ Parses the request content into `self.data`. """ if not _hasattr(self, '_data'): self._data, self._files = self._parse() #执行self_parse(),获取解析器，并对content_type进行解析，选择解析器，返回数据 if self._files: #判断文件流数据，存在则加入到self._full_data（也就是我们的request.data）中 self._full_data = self._data.copy() ， self._full_data.update(self._files) else: self._full_data = self._data #不存在将无文件流的解析完成的数据赋值到self._full_data(request.data) # if a form media type, copy data & files refs to the underlying # http request so that closable objects are handled appropriately. if is_form_media_type(self.content_type): self._request._post = self.POST self._request._files = self.FILES
进入self._parse()源码
def _parse(self): """ Parse the request content, returning a two-tuple of (data, files) May raise an `UnsupportedMediaType`, or `ParseError` exception. """ media_type = self.content_type #获取请求头content-type try: stream = self.stream #获取请求体 except RawPostDataException: if not hasattr(self._request, '_post'): raise # If request.POST has been accessed in middleware, and a method='POST' # request was made with 'multipart/form-data', then the request stream # will already have been exhausted. if self._supports_form_parsing(): return (self._request.POST, self._request.FILES) stream = None if stream is None or media_type is None: if media_type and is_form_media_type(media_type): empty_data = QueryDict('', encoding=self._request._encoding) else: empty_data = {} empty_files = MultiValueDict() return (empty_data, empty_files) parser = self.negotiator.select_parser(self, self.parsers) #选择解析器 if not parser: raise exceptions.UnsupportedMediaType(media_type) try: parsed = parser.parse(stream, media_type, self.parser_context) #执行解析器的parse方法 except Exception: # If we get an exception during parsing, fill in empty data and # re-raise. Ensures we don't simply repeat the error when # attempting to render the browsable renderer response, or when # logging the request or similar. self._data = QueryDict('', encoding=self._request._encoding) self._files = MultiValueDict() self._full_data = self._data raise # Parser classes may return the raw data, or a # DataAndFiles object. Unpack the result as required. try: return (parsed.data, parsed.files) except AttributeError: empty_files = MultiValueDict() return (parsed, empty_files)